The New Delhi Television news channel says at least one person was killed in the collapse in the eastern city of Kolkata. Photo / NDTV

Rescuers in Kolkata dug through large chunks of debris from an overpass that collapsed while under construction, killing at least eight people and injuring scores of others in trapped cars, trucks and other vehicles, officials said.

Army troops joined efforts to rescue those trapped inside vehicles that lay under massive concrete blocks and metal debris. Huge cranes and other rescue vehicles reached the site to clear the rubble.

The Press Trust of India news agency, quoting police sources, put the death toll at eight. More than 40 injured were admitted to two hospitals in Kolkata, the capital of West Bengal state, hospital officials said.

“The area was very, very crowded. Motorized rickshaws, taxis … there was a lot of traffic,” one witness told the New Delhi Television news channel, or NDTV.

Another added: “We heard a loud rumble and then saw a lot of dust in the sky.”

Television images showed the bloody legs of some of the trapped people jutting out of the collapsed girders and concrete slabs

In addition to army troops, personnel of the National Disaster Response Force also worked on the scene in Bara Bazaar, a busy residential and shopping area in central Kolkata.

O.P. Singh, the NDRF chief, said the operation was a “very, very challenging task.”

Building collapses are common in India, where builders use poor enforcement of regulations and use substandard materials.